1. Field
The present invention pertains to semiconductor devices, and is particularly directed toward the fabrication of true complementary devices in monolithic integrated circuits (ICs).
2. Prior Art:
Various methods have previously been proposed and used in an effect to fabricate complementary devices in a single substrate. To date, none has proved entirely successful to produce true complementary devices such as PNP and NPN bipolar transistors, in the sense that the transistors possess closely similar or matching electrical characteristics including collector resistivity, base resistivity, base penetration, base width, and emitter resistivity. Some integrated circuits are entirely formed within a wafer of single crystal semiconductor material, and what is effectively the substrate of many of the incorporated devices is typically used as the collector region of one type of bipolar transistor. It is virtually impossible to fabricate complementary transistors in such structures.
Techniques heretofore proposed for producing complementary transistors include those disclosed in U.S. Pat. No. 3,473,090 issued Oct. 14, 1969 to Bohannon, U.S. Pat. No. 3,474,308 issued Oct. 21, 1969 to Kronlage, and U.S. Pat. No. 3,576,682 issued Apr. 27, 1971 to Frouin et al.